Manufacture of alloys

ABSTRACT

THIS INVENTION RELATES TO THE INTRODUCTION OF A CONTROLLED QUANITY OF A HIGH MELTING COMPONENT INTO A MELT OF A LOW MELTING BASE METAL. THIS IS EFFECTED BY FEEDING A ROD OF THE HIGH MELTING COMPONENT INTO THE ABOVE MELT, WHILE THE SAID ROD IS SUBJECTED TO A SONIC VIBRATION, AND AT THE SAME TIME, THAT PORTION OF THE ROD PROTRUDING ABOVE THE LEVEL OF THE MELT IF COOLED. THIS MELT ENSURE THAT THE MANUFACTURE OF ALLOYS IS EFFECTED WITH GREAT ACCURACY, SIMPLICITY AND ECONOMY.

July 13, 1971 R POHLMAN EI'AL 3,592,636

I MANUFACTURE OF ALLOYS Filed Oct. 28, 1968 5 Sheets-Sheet 1 July 13, 1971 POHLMAN ETAL 3,592,636

MANUFACTURE OF ALLOYS Filed Oct. 28, 1968 3 Sheets-Sheet Fig.2

July 13, 1971 P HL ET AL 3,592,636

MANUFACTURE OF ALLOYS Filed Oct. 28, 1968 3 Sheets-Sheet 5 Fig. 4

United States Patent 3,592,636 MANUFACTURE OF ALLOYS Rermar Pohlman, Aachen, Kiaus Groove, Neuss, and Walter Fichtl, Buttgen-Vorst, Germany, assiguors to Groove & Welter, Neuss, Germany Filed Oct. 28, 1968, Ser. No. 771,028 Claims priority, application Germany, Oct. 31, 1967, G 51,503 Int. Cl. C22c 1/00 US. Cl. 75-135 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to processes for the introduction of controlled quantities of higher melting metal components into low melting base metals under the action of sonic vibrations.

The alloying of metals normally requires several process steps, especially since with higher melting components long dissolving times are necessary, and accuracy of the desired alloying concentration cannot generally be attained in one melting process. The procedure is thus first to manufacture a pre-alloy of higher concentration and this is immersed, either fluid or solid into a melting bath in which the finished alloy is produced. In this, a control analysis of the concentration of the alloy obtained is generally necessary, since metal losses, eg by burn off of the product, can occur. The manufacture of alloys with very small concentrations of alloying components presents, for these reasons, special difficulties.

It has already been proposed to assist in overcoming the poor solubility of high melting metals in low melting base metals by the action of ultrasound. It is, for example, known to manufacture metal alloys using ultrasound, in which the alloying components are converted by known means into the liquid phase and finally vibrated with the object of homogenising or dispersing the individual metallic components. In this, technique, the ultrasonic generator either engage on the wall of the melting vessel or dips into the melt itself.

It is also known to excite the melt itself, or the crucible, to high frequency sonic vibrations by electromagnetic or electrodynamic methods. Low frequency vibration generators for melts are also known, which work in the audible region or act by the generation of shock waves on the surface of the melt.

A method for the homogenisation of a melt by ultrasonic excitement has also been described in which at least one of the fluid alloy components is blown into the other component or components by a pipe or nozzle arrangement. Finally, attempts have been made to build a body of alloying metal into the floor or a melting vessel so that on excitement by ultrasound of the fluid melt surrounding it, it is dispersed or dissolved. It has also been proposed, without the use of ultrasound, to make possible a one-step alloying process by introducing a measured amount of fluid alloying metal into the base metal by means of special apparatus.

The known processes of ultrasonic treatment of metal melts are intended primarily to achieve a reduction in the grain size of the structure. They are neither designed for,

3,592,535 Patented July 13, 1971 nor suitable for, effecting a controlled adjustment of the desired content of higher melting metal component in lower melting base metal.

It is an object of the present invention to provide a process, which enables the accurate manufacture of metal alloys in one process step, without the use of pre-alloys being necessary, and whereby an accuracy may be achieved which makes control analysis prior to casting unnecessary. The invention has for its special purpose that of enabling an introduction or exact dosing of alloying components of high melting point into a base metal of low melting point in simple and economic fashion.

According to the present invention there is provided a process for introducing a controlled quantity of a high melting metal component into a melt of a low melting base metal which comprises feeding a rod of the high melting component into the said melt while subjecting the said rod to sonic vibration and at the same time cooling the rod which extends above the surface of the melt. According to a further feature of the invention the rate of cavitation-produced solution of the metal rod thus achieved is controlled by adjustment of the depth of immersion of the rod in the melt and by adjustment of the exciter frequency of an oscillation generator used to provide the sonic vibration.

According to a particular embodiment of the process according to the invention, during the immersion of the rod, the excitation frequency of the vibration generators is automatically made to be the natural frequency of the vibration system, varying during solution, of the rod.

As sonic vibrations, ultrasonic vibrations are preferred, and the invention will therefore be explained especially with reference to the use of ultrasonic vibrations.

In the process according to the invention at least the lowest part of the vibration system is constituted by a rod of the metal to be introduced, which on excitation with a definite ultrasonic energy dissolves on immersion in the melting bath, the solution of the material of the rod caused by cavitation being so controlled that an optimum dissolution velocity and a regular dissolution of the immersed portion of the rod are obtained. The control of various factors influencing the vibration treatment makes possible a large scale use of the process, from which it follows, in an economic fashion, i.e. in a short time, that reproducible results of greater accuracy can be obtained.

By the immersion of the rod, which constitutes a part of the ultrasonic system, the rod itself tends to become very strongly heated, as a result of its high thermal conductivity. This circumstance causes an increase in the damping of the vibration, with consequent reduction in the solution velocity. By shorting the rod as a result of dissolution, the natural frequency of the whole system changes, and this again reduces the solution velocity. It is optionally desirable so to control the solution of the immersed rod, that the rod shortens itself at a constant cross-section and that metal removal takes place only at the face of the end of the rod. Without such control there is a tendency for metal to be removed from the lateral surface(s) of the rod and this can lead to pieces of the rod breaking away and either sinking or floating in the melt as not yet dissolved compact pieces of metal.

When this occurs accurately dosed additives of the rod metal are impossible to achieve.

Surprisingly, success has now been obtained, by the process of the present invention, in the control of the foregoing contrary influences on the direct vibration of the metal to be introduced, so that a maximum dissolving power of the metal, with a high rate of removal and a minimum alloying time, can be obtained, and so that the process is effective for large-scale use. In the process of the present invention the higher melting metal component is introduced from above into the melt of the lower melting component, as an automatically tuned ultrasonically excited vibration element, cooled until just above the melt surface, with a drive corresponding to the solution rate, and is dissolved therein.

The intensity of the ultrasonic excitation is of great importance. In a practical embodiment there is used for carrying out the process, an apparatus, the essential components of which consist of a compound rod-shaped vibration system, which includes a rod, preferably of several half-wavelengths long, of especially low acoustic damping, and integrally connected thereto, a similarly rodshaped piece of the metal to be vibrated and and adjustable advancing device. The compound rod-shaped vibration system is held at two points in as damping-free a way as possible, and is cooled in the working position to just above the melt surface. By this construction, it is effected that in the rod of several half-wavelengths length of specially low acoustic damping, substantially the whole of the ultrasonic power is led, substantially without loss to the shorter piece of the metal, connected to its end, which is to be vibrated.

Preferably, the compound vibration system is excited with the aid of ultrasonic exciter, intensively at its natural frequency, and so that the rod is led in a vertical guide by means of a infinitely variable regulatable drive into the lower melting components in molten state, from above, with a speed which corresponds to the dissolution speed of the metal of the rod.

Since the ultrasonically excited vibration system shortens during running, by dissolution of the metal of the rod, and thus the natural frequency increases by the same degree, the rod of length several half-wavelengths is suitably provided at the excitation end with a pickup, which controls the high frequency generator serving for the excitation in such fashion that the excitation frequency of the generator automatically follows the varying natural frequency of the vibration system. The ultrasonic excitation thus remains constant despite the dissolution and shortening of that part of the rod dipping into the melt.

According to another embodiment of the invention, the excitation frequency can also be controlled by a time or weight regulated device, which for .a constant dissolution velocity also shortens the vibration element with a constantly maintained speed. The control of frequency can result in simple fashion from the constant decrease in the weight or buoyancy of the vibration element dipping into the melt.

The dissolution velocity of the metal of the rod increases, for a given sonic power, with increasing temperature of the metal of the rod and of the surrounding melt of base metal. On the other hand, however, the ultrasonic transfer in the metal of the rod decreases with rising temperature, so that insutficient sonic power is obtained at the face of the rod. In order to obtain an optimum dissolution velocity a well determined cooling of the rod, and therewith an optimum temperature reflection at the face, is of decisive importance. In order to obtain an especially high dissolution velocity, this material-dependant temperature reflection should be kept as high and as constant as possible.

This requirement can be realised by carrying out the process according to the invention so that the melt of base metal or the rod of the metal to be introduced are constantly and regularly moved relative to one another, in that for example, the vibrated rod is introduced into the melt in an electric induction furnace. A device can also be provided which allows a reciprocatory or circular movement of the immersed rod.

The process of the present invention and an embodiment of apparatus for use therein is illustrated by the accompanying drawings.

In FIG. 1 of the drawings there is illustrated an example of an apparatus according to the invention. A sonic or magnetostrictive ultrasonic generator is designated 1,

which is surrounded by a housing 1a, and which, for example, can operate in the region between 5 and 60 kc./s. It is rigidly connected to a rod 2 of length greater than half a wavelength, to the lower end of which a rod-shaped piece 3 of an alloy metal to be vibrated is attached, e.g. screwed to the rod 2, as is indicated by 18. The resulting composite ultrasonically excited vibration system can be driven via a spindle 4 with the aid of a drive 5, driven by an electric motor and adjustable infinitely variable, on sliding collars 6 along a vertical guideway 7 (having three columns), into the melt 8, or, after ending of the process driven out again in fast drive. On the excited end of rod 2 there is attached a pickup 9, which can control the high frequency excitation generator.

The whole apparatus is mounted on the lid 10 of a melting crucible 11 and extends through an opening in the lid 10 into the melting chamber of the crucible 11, the end of the rod 3 of alloy metal dipping into the melt of base metal 8. The ultrasonic exciter 1 is sprayed with a cooling agent such as cooling water by a spray 12. If necessary, it can also be cooled by the use of a gaseous cooling agent. The spray cooling provided is essentially more advantageous than, for example, a conventional immersion cooling in water, because in the latter a great deal of the acoustic power generated is led away to the surrounding water and housing, which is not the case in a spray process. The rod-shaped sonic transmitter 2 is led through into the housing 1 or by means of or through an opening having an elastic seal 13. The seal 13 can, for example, consist of a rubber ring, and is on the one hand especially poor in damping and thus removes almost no energy from the vibrating system, and on the other hand allows the reliable collection of the cooling water, which can be led away via apipe 14.

A further spray 12 is provided for trapping the heat conducted up from the melt 8 and the radiated heat, which is arranged in a vessel 15 surrounding the joint between rod 2 and rod 3, by means of which the water running away can be caught by a holder and seal 13. A suction tube 14 serves to maintain the water level low, in order to avoid ultrasonic dissipation in the vessel 15. The vessel 15 is surrounded by a polished reflective housing 16, and at its base is isolated from the housing 16 by means of an intermediate asbestos ring 17, so that both heat radiation and heat conduction are greatly diminished.

In the apparatus according to the invention, thermal differences between the metal rod 3 and the rod 2 are avoided by cooling of the joint with which the rod 3 of the alloying metal is acoustically rigidly joined to the rod 2, so that the acoustic transfer at this point is held very constant.

An especial advantage of the apparatus according to the invention consists in that each part of the system which is important for good transfer of the high ultrasonic power remains cool and thus free of damping, despite the heat lost from the ultrasonic exciter from above and the heat conducted away from the melt.

A further advantage of the apparatus according to the invention can be seen in that a large relative change of the rod 3 introduced into the base metal melt, results in only a small relative change, and thus a controllable frequency change of the whole vibration system, consisting of the ultrasonic exciter 1, the vibration transmitter 2 and the rod 3.

The rod 3 can be constructed in various way. The rod can be solid, or in some cases hollow. The rod can consist of two or more alloy components. Further, particular sections or annuli of the alloying metal rod can consist of different materials.

FIG. 2 shows schematically the circuit principles of automatic frequency control for an ultrasonic generator. The ultrasonic generator is designated 1 and a rod more than several half wavelengths long serving as vibration conductor is designated 2, to the end of which is joined a rod shaped piece of alloying metal to be vibrated (here not shown). A pickup 9 is fixed to the excited end of rod 2. The pickup 9 (electromagnet transducer) transmits electrically the feed back voltage taken from the rod 2 to a device 19 for automatic resonance tuning. In device 19 the feedback voltage is amplified, before it is led to the high frequency generator 20', and the phase is corrected by a phase adjuster, so that the high frequency excitation and the ultrasound oscillate in phase.

In FIGS. 3 to 6 there are illustrated four rod pieces of vibrated, or to be vibrated, alloying metal in transverse section.

In FIG. 3 the rod piece 21 of alloying metal has a thread 18 on its upper end, which can be screwed into a rod 2 serving as vibration conductor (FIG. 1). At its lower face 22, metal is dissolved from rod piece 21 in a metal melt by the action of the ultrasonic vibrations. The face 22 is almost evenly worn away, and shows only a rough surface caused by the action of cavitation consisting of many small craters. The rod piece 21 is, according to the process of the invention, regularly cooled down to just above the molten melt.

In FIG. 4 there is shown a corresponding rod piece 23 of alloying metal, as is obtained by dipping the rod piece of alloying metal excited by ultrasonic vibrations without the application of cooling. It is clearly evident that the metal removal at the face 24 is wholly irregular.

FIG. 5 shows a rod piece 25 which is constructed from two different alloying metals. The rod piece 25 has an outer sleeve portion 26 of an alloy X and a core piece 27 of an alloy Y.

FIG. 6 shows a rod piece 28 of alloying metal which is hollowly constructed. The upper end of the tubular rod is closed and bears the thread 18, which is screwable into the rod 2 which acts as a vibration conductor.

The advantages of the method of the invention are multiple: It allows the manufacture, as mentioned above, of alloys in which the great difference between the melting points of the alloy components would lead in conventional alloying to an uneconomically high burnotf, and it achieves this without the use of protective gas, which substantially eases the working conditions. Additionally, the process according to the invention allows an excellent control of the dosage of the rod metal, especially when the closely controllable apparatus described is used. This dosage is accurate since both the time of vibrating, and the intensity of the ultrasonic excitement, can be adjusted to zero, and without vibration the higher melting component practically does not dissolve in the lower melting component over a short period of time. On the basis of this exact dosage possibility, there appears the further advantage that the normally necessary analysis of the pre-prepared alloy can be avoided. The process makes it possible to establish a very high degree of homogeneity and to obtain very fine and regular dispersions, even with metals of very different density.

The process and apparatus according to the present invention are thus suitable for accurate and rapid alloying, especially for small alloying concentrations. In the known alloying art, one is compelled after alloying a small concentration of alloying metal, e.g. a concentration of less than 1%, to take a test for control analysis prior to pouring the melt, wherein one strives toward the lower limit of content in the base metal, in order, if necessary to be able to correct the concentration by additional alloying. However one generally proceeds in such fashion that one first manufactures a pre-alloy of higher concentration, casts this alloy to slabs or bars, in order then in the manufacture of the final alloy, to achieve an accurate end alloy with the aid of the pre-alloy slabs. However, control analysis before casting is still not unnecessary, since varying metal losses can arise, especially in multitage alloying processes.

Compared to this, by the application of the present invention, the direct and accurate manufacture of alloys is made possible, without the diversions of prealloys, alloying corrections and subsequent analysis having to be taken. Thus, for example, rods can also be alloyed into a base melt by direct vibration, which consist of one metal alloy or of several metals put together in sections, so that a multicomponent alloy can be manufactured in one process. Especially for the NE-metals, e.g. zinc, even the smallest alloying concentrations, from a few hundredths to a few tenths of a percent, may have a pronounced effect on the properties. Thus, for example, the ageing resistance of zinc-copper alloys can be importantly influenced by an iron or titanium content of 0.02%.

The following example will serve to illustrate the invention.

EXAMPLE This example illustrates the manufacture of a zinc alloy of pure zinc with 0.15% titanium and 0.60% copper.

In the screw hole of the exciter rod 2 of an apparatus according to the drawing there was screwed a rod of titanium of diameter 50 mm. having one end threaded. In the same way, a correspondingly prepared rod of copper of diameter 50 mm. was joined to the exciter rod 2 of a second apparatus. Both units of apparatus were at the same time inserted with their alloying rods of titanium and copper into a melt of pure zinc, a charge of 300 kg. of which has been heated to atemperature of 600 C. in an electric induction furnace, the distance of the surface of the melt from the floor of the vessel being a few centimetres. The advance rate of the alloying rods 2 was set at 4 mm. per minute. The original frequency of the ultrasonic exciter amounted to 20 kc./s., the average intensity to 10.7 w./cm. In operation, the exciter frequencywas matched to the varying natural frequency of the vibration system (1,2,3).

After a vibration time of 12 minutes, the apparatus with the titanium rod was removed from the melt, and after a time of 24 minutes that with the copper rod was removed. Thereafter the contents of the furnace were teemed, cast to rolling slabs, and these rolled out to bands. Analysis gave an accurate content of the alloy required, of 0.60% copper and 0.15% titanium, and the technological properties of the sheet metal made from this alloy were found to be completely homogeneous.

The rods illustrated in FIGS. 3 and 4 consist, for example, of titanium with a purity of 99.4% Ti and 0.25% Fe and are suitable for the manufacture of a zinc-titanium alloy.

For manufacture of a multicomponent alloy, the rods in FIGS. 3 and 4 can consist, for example, of a nickelchromium alloy with 76% nickel and 15% chromium.

The rod in FIG. 5 consists, for example, of a sleeve portion 25 of pure aluminium with a purity of 99.5% Al, while the core is constructed of magnesium with a purity of 99.8% Mg. This rod is provided for the manufacture of a zinc-aluminium-magnesium finished alloy.

The rod of FIG. 6 consists, for example of magnesium with a purity of 99.8% and is tubularly constructed, in order, for example, to attain very precise dosages by means of a decreased rod face area, and also, if necessary, to serve as a bell filled with protective gas.

We claim as our invention:

1. A process for introducing a controlled quantity of a high melting metal component into a melt of low melting base metal which comprises feeding a rod of the high melting component into the said melt while subjecting the said rod to sonic vibration and at the same time cooling the part of the rod which extends above the surface of the melt.

2. A process according to claim 1 wherein the rate of cavitation-produced solution of the metal rod thus achieved is controlled by adjustment of the depth of immersion of the rod in the melt and by adjustment of the frequency of the sonic vibration.

3. A process according to claim 1 wherein during said immersion of the rod the frequency of the vibration is automatically adjusted to be the natural frequency of the vibration system as it alters during dissolution of the rod.

4. A process according to claim 1 wherein during the immersion and dissolution of the rod, the rod over the surface of the melt, and the joint between the vibration transmitter and the rod, is cooled.

5. A process according to claim 4 wherein during immersion and dissolution of the rod the means provided to establish the vibration is itself cooled.

6. A process according to claim 1 wherein between the vibrated rod and the melt a regular relative movement is efiected.

7. A process according to claim 1 wherein the rod consists of a multi-com'ponent alloy.

UNITED STATES PATENTS 2,595,292 5/1952 Reece 75-135X 2,786,755 3/1957 Paddock et al. 75l68 3,275,787 9/1966 Newberry 7565X 3,362,854 1/1968 Tanabe 148-l2.9

L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant Examiner US. Cl. X.R. 75178 

